Wireless telecommunications systems are divided into a series of cell areas covering a service area. Each cell area has a transmitting base station using its own operating frequency set comprising a plurality of radio channels to communicate with mobile subscribers. Each channel represents an information signal at a particular frequency carrier or band.
It has been found advantageous to combine these channels for transmission purposes. The channels are all combined by a broadband signal combiner into a multi-channel signal at low power levels and then amplified by a single linear amplifier (or its equivalent a plurality of linear amplifiers in parallel, each amplifying a reduced power version of the same multi-channel signal) to raise the multi-channel signals to an appropriate transmit power level.
The various radio channels are distributed in frequency with respect to each other in that each operates within a different frequency band. Simultaneous occurrence of individual signal peaks readily occur and hence the multi-channel signal is subject to power maximums where the peak power significantly exceeds the average power of the envelope due to constructive addition of the individual signal peaks.
A straight forward response to this problem has been to select the power rating of the linear amplifier to accommodate the theoretical maximum peak power level of the composite multi-channel signal. However, this significantly increases the cost of the linear amplifier since its power rating must be increased in proportion to the square of the number of signals processed. This high power rating is also only needed for a small fraction of the operating time of the amplifier (that is, during the high peaks of the combined multi-channel signal). It is desirable to operate the system with amplifiers of power handling ratings based on the average power of the sum of the carriers than to require that an amplifier be rated to handle the extreme high peak power caused by the constructive addition of the individual carriers.